Strip gage change during rolling in a tanden rolling mill

ABSTRACT

Method and apparatus for changing the gage of strip material being rolled on a tandem rolling mill while the strip is in motion and moving through the mill. This is accomplished by changing, in timed sequence, the stand speed and roll gap openings starting from the first to the last stand. In order to change gage during rolling, the roll gap opening and speed of the first stand are initially changed. This causes a change in interstand tension between the first and second stands which, in turn, is sensed and used to vary the roll gap of the second stand. Next, the speed of the second stand is changed. This causes a change in interstand tension between the second and third stands; whereupon the speed of the third stand is varied, and so on, until all roll gaps and stand speeds have been varied to accommodate the new gage.

United States Patent [191 Connors Apr. 30, 1974 1 STRIP GAGE CHANGE DURING ROLLING IN A TANDEN ROLLING MILL V [76] lnventor: John J. Connors, 5060 Elmcroft Ct.,

Clarence, NY. 14031 [22] Filed: Sept. 29, 1972 [21] Appl. No.: 293,618

52 us. C1. 72/8 [51] Int. Cl B2lb 37/00 [58] Field of Search 72/9, 8, ll, 12, 16

[56] References Cited UNITED STATES PATENTS 3,603,124 9/1971 Arimura et al. 72/8 3,727,441 4/1973 Morooka et a1. 72/6 Primary ExaminerMilton S. Mehr Attorney, Agent, or Firm-J. J. Wood ABSTRACT Method and apparatus for changing the gage of strip material being rolled on a tandem rolling mill while the strip is in motion and moving through the mill. This is accomplished by changing, in timed sequence, the stand speed and roll gap openings starting from the first to the last stand. In order to change gage during rolling, the roll gap opening and speed of the first stand are initially changed. This causes a change in interstand tension between the first and second stands which, in turn, is sensed and used to vary the roll gap of the second stand. Next, the speed of the second stand is changed. This causes a change in interstand .te'nsion between the second and third stands; whereupon the speed of the third stand is varied, and so on, until all roll gaps and stand speeds have been varied to accommodate the new gage.

4'Claims, 2 Drawing Figures 5.2 5.1 g i 28 M 7 l8 42 (D G) G) T1 T2 T3 T4 7 170p Ml M2 E M3 M4 H5 M5 30 rcz {T63 ,Tc4 Tcs GAGE TENSION TENSION TENSION TENSION CONTROL CONTROL CONTROL CONTROL CONTROL TEN TEN TEN f32 REF i REFI42 REFl 3e SPEED SPEED SPEED SPEED SPEED 34 g CONTROL cl CONTROL c2 CONTROL \ca CONTROL RC4 CONTROL v I 1 24 g 1 RI R2 I R3 R4 R5 1 g GAGE I i I CONTROL I 38 I 22 (LP/22 I I 44 48 I I so? I v 1' I 1 26\ 2o GAGE CHANGE SEQUENCER MASTER SPEED CONTROLLER l STRIP GAGE CHANGE DURING ROLLING IN A TANDEN ROLLING MILL BACKGROUND OF THE INVENTION In the operation of prior art tandem rolling mills, it has been necessary to roll the entire length of metal strip material in one coil to a single specified thickness. That is, there has been no satisfactory way of changing gage while the strip material is inmotion. One complete coil had to be rolled to a specified thickness; and the roll gap and speed settings then changed for the respective stands while the mill was not in use and before a succeeding coil was rolled to a different gage. As a result, small single coil orders of different gages meant small coils with a resultant reduced production efficiency. Furthermore, it has not been possible with prior art systems to weld together several lengths of strip material of varying thicknesses and roll them to a constant, final gage.

SUMMARY OF THE INVENTION or lengths of strip of varying gages can be welded togetherand rolled to a single, uniform thickness.

Specifically, there is provided a method for changing the gage of strip material being rolled in a multi-stand tandem rolling mill wherein the roll gap setting and speed of the first stand are initially changed to change the gage of the strip material issuingfrom the first stand. Thereafter, in timed sequence, the roll gap settings and speeds of succeeding stands are changed until all roll gap settings and speeds of the stands in the mill have been changed to accommodate a new gage. The roll gap setting and speed of each stand following the first is changed after a change in the immediately preceding stand .following a time interval substantially equal to the time required for the strip to travel to each stand from its immediately preceding stand. In this manner, the length of the strip material over which a transition in gage occurs is minimized. The points at which a transition in gage occurs can be automatically 2 J panying drawings which form a part of this specification, and in which:

FIG. 1 is a block schematic diagram of one embodiment of the invention; and

FIG. 2 is a plot of time versus strip speed and thickness for each of five stands in a tandem mill showing the manner in which the gage and speed are changed in each stand.

With reference now to the drawings, and particularly to FIG. 1, the system shown includes a five-stand tandem rolling mill including stands S1, S2, S3, S4 and S5. Each stand comprises a pair of work rolls and 12 between which strip material being rolled passes, together with a pair of backup rolls, not shown. The strip issuing from the last stand S5 is wound on a coiler 16, the direction of strip movement being from left to right as indicated by the arrow 18 in FIG. 1.

The rolls of each stand are driven by means of drive motors M1, M2, M3, M4 and M5 each controlled by a speedcontrol circuit C1, C2, C3, C4 and C5, respec tively. The speed control circuits C1-C5, in turn, are connected to a master speed controller 20 which establishes a nominal or desired speed for each of the stands in the mill to achieve adesired gage reduction. In this respect, and since each of the stands in the mill is reducing the'strip in thickness, the speed of the material issuing from any stand must be greater than that entering the stand in accordance with the constant volume principle. Accordingly, the speed of stand S2 must be greater that of stand S1; the speed of stand S3 must be greater than that of stand S2, and so on the speed of stand S5 beinggreatest.

Note that the lead or conductor connecting each of recorded and a single coil thereafter severed at the tively minor portions of the strip over which a gage transition occurs.

In the preferred embodiment of the invention, interstand tension is sensed and used to control the roll gap of a succeeding stand. In this manner, when the gage of the first stand is changed, for example, a tensiometer between the first and second stands will immediately sense a change in tension and will, through an appropriate control loop, change the gap of the second stand to accommodate the new gage. This occurs automatically as the gage changes at the outpu t of each stand without requiring any sequencing circuitry. It is, however, necessary to provide sequencing circuitry to change the speed of succeeding stands such that the change in gage occurs at essentially the same point or location on the strip as it travels through the tandem mill.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accomcontroller 20 includes a motor operated rheostat, the

rheostats being identified as R1, R2, R3, R4 and R5,

respectively. With reference to rheostat R1, for example, it includes a motor 22 connected to a movable tap 24. The motor 22, in turn, is connected to a gage change sequencer 26, the purpose of which will hereinafter be explained. It will be understood, of course, that as the taps 24 on the rheostats Rl-RS are varied, the speeds of the stands 51-85 will also be varied from that speed initially established by the master speed controller 20.

In the embodiment of the invention shownherein,

the chocks supporting the rolls in each stand are loaded by means of hydraulic cylinders H1, H2, H3, H4 and H5, respectively. That is, the hydraulic cylinders I-Il-I-IS provide the necessary roll force to reduce the strip 14 in thickness; and while only one cylinder is shown for each stand in the schematic illustration of FIG. 1, it will be understood that in an actual rolling mill there are hydraulic cylinders on opposite sides of the mill loading each of the chocks at the opposite ends of the rolls. It is, of course, possible to use a mechanical screwdown mechanism or a wedge-type control to effect somewhat the same results; however hydraulic cylinders are preferred because of their speed of operation.

The gage of strip material passing through the first stand S1 is measured by means of an X-ray gage 28 or the like. Gage 28 produces an electrical signal proportional to the actual gage between stands S1 and S2; and this signal is applied to a gage control circuit 30 where it is compared with an electrical signal proportional to desired exit gage from stand S1. This reference signal,

on lead 32, is delivered from a motor-driven potentito a motor 38 controlled by the gage change sequencer 26. If the actual gage at the output of stand S1 does not match the desired gage as determined by the position of tap 36 on potentiometer 34, then the gage control circuit 30, through appropriate hydraulic controls, not shown, either increases or decreases the pressure on cylinder H1 to increase or decrease the roll force and- /or roll gap and thereby vary the gage of material issuing from stand S1 until it matches the desired gage.

Between successive ones of the stands are tensiometers T1, T2, T3 and T4 which measure tension in the strip between each set ofstands. The tensiometer T1, for example, measures the tension in the strip material 14 between stands S1 and S2 and produces an electrical signal proportional thereto. This tension signal from tensiometer T1 is compared in tension control circuit TC2 with a tension reference signal on lead 40 propor tional to desired tension; and if the two are not the same, then the tension control circuit TC2, through appropriate hydraulic controls, not shown, will vary the pressure exerted by cylinder H2 for stand S2, thereby varying the roll gap opening and/or roll force of stand S2. Similar tension control circuits TC3-are provided for stands S3-S5, respectively. Each t'ensiometer measures the interstand tension and compares it with a tension reference signal; and if the two are not the same, then the roll gap opening for the succeeding stand is varied.

Let us assume, for example, that the tension between stand S2 and S3 increases. Under these circumstances, comparison of the increased tension signal from tensiometer T2 with the tension reference signal on lead 40 will act to decrease the roll gap of the rolls on stand S3 until'the tension is reduced to the desired value. Similarly, if the tension between stands S2 and S3 should- 'of an X-ray gage 42 or the like which producesan elec-' trical signal proportional to actual, measured output gage. This is applied to a gage control circuit 44 where it is compared with a signal proportional to the desired gage or thickness as derived from a potentiometer 46.

As shown, potentiometer 46 has a movable tap 48 connected to a drive motor 50, the motor 50 being connected to the gage change sequencer 26. If the actual output gage does not match the desired gage as established by the tap 48 on potentiometer 46, then the gage control circuit 44 will apply an error signal to the speed control circuit C' to either increase or decrease the speed of motor M5 in stand S5 to correct for a variation from desired gage. Alternatively, the output error signal from the gage control circuit 44 can be applied to the tension control .circuit TC5 to either increase or decrease the roll gap of the last stand S5. In most cases,

- however, speed control for varying final output gage is desired on the last stand.

The system thus far described is more or less conventional. As was explained above, mills of this type normally operate by rolling a continuous length of strip on a coil to ,a single specified thickness or gage along the entire length of the strip. However, situations arise where it is desired to'change the gage of the strip material on a single coilwhile it is in motion and being rolled. As was explained above, this may happen, for example, on small orders where, in the past, it has been necessary to roll a single coil of strip material of limited length. This requires shutting down the mill between successive, small coils, and resetting the speed and gage references after each coil is rolled.

In accordance withthe present invention, and as was explained above, a gage change is effected during rolling by initially changing the roll gap setting and speed of the first stand S1 to change the gage of the strip material issuing from the first stand. Thereafter, in timed sequence, the roll gap settings and speeds of succeeding stands are changed until all roll gap settings and speeds of the stands in the mill have been set to accommodate a new gage. In thisrespect, it is necessary'only to change the gage references to stands S1 and S5 since these are the only stands at which output gage is measured. On all other stands, it is necessary only to externally change the speed of the stand. The roll gap opening of the stands following the first stand is automatically varied by means of the tension control circuits TC2-TC5.

Assuming that the gage of the strip material is to be reduced during rolling, the gage change sequencer circuit 26 will initially drive motor 38 for rheostat 34 and motor 22 for rheostat R1 to decrease the roll gap of stand S1 and increase its speed. As the roll gap is decreased, the speed must be increased in accordance with the constant volume principle. Following the change in roll gap setting and speed of stand S1, and after a time interval approximately equal to the time required for a point on the strip to travel from stand S1 to stand S2, the gage change sequencer 26 will drive the motor 22 0f potentiometer R2 to increase the speed of stand S2. This, in turn, increases the tension between stands S1 and S2; whereupon the tension control circuit TC2 will decrease the roll gap of stand S2 until the desired tension is again maintained. This process is repeated for stands S3-S5 until the'speeds of all stands have been increased and their roll gaps decreased to effect a change in final output gage. It should be noted that when material of changed gage reaches stand S5, the setting of potentiometer 46 is varied via motor 50 and gage change sequencer 26 to reflect the new, de-

sired output gage. The gage change sequencer, of course, may take various forms well known to those skilled in the art and is essentially a timing device. Pushbuttons, a computer or'the like can be utilized to initiate the sequencing of circuit 26 to effect a change in gage.

Referring to FIG. 2, it represents a plot of time versus strip speed and thickness for each of the five stands in a tandem mill. The stands are shown in simplified form to facilitate understanding and the time calibration is not necessarily constant from left to right. FIG. 2 portrays a situation where delivery gage is to be increased in thickness. The following Table I shows the original rolling schedule while Table II shows the revisedrolling schedule:

TABLE I ORIGINAL ROLLING SCHEDULE 4.0 MM input thickness to 1.0 MM output Stand 1): H,-

TABLE II REVISED ROLLING SCHEDULE Multiply all drafts by ratio of D /D 2.9 MM/3.0

to change output gage from 1.0 MM

to 1.1 MM same input; thickness of 4.0 MM

Stand D, H, S

1 .966 3.034 .330 2 .966 2.068 .484 3 .58 1.488 .673 4 .29 l.l98 .834 5 +.O98 LI .909

In the foregoing tables, H represents the output gage at the respective stands, 5,, represents the output speed at the respective stands, D is the draft in each stand is defined as the difference between input and output thickness; and D, is the total draft of the mill. All of this is based upon the constant volume principle, assuming constant width wherein:

The sequence is as follows: At time 13,, it is decided I to change the gage of thestrip that is at that instant in stand S1. The stand speed is reduced as shown in FIG. 2 and the set-point for the gage is changed. This occurs, with reference to FIG. 1, by changing the positions of the movable taps on rheostats 34 and R1. Thus, at time 2,, the thickness H 'of strip issuing from the stand S1 increases and the speed S of stand S1 decreases. Immediately, stand S2 tension regulator TC2 operates on the stand S2 cylinder H2 to maintain tension. The amount of strip between the start of a gage change and the point at which the correct gage is rolled on stand S1 at the desired speed is referred to as transitional strip. This transitional strip is off-gage strip and is shown in FIG. 2 as A H,, A H and so on. However, the tension regulators will maintain set tension during the time this transitional strip is being rolled.

At time t in FIG. 2, the strip tracking system established by the gage change sequencer 26 indicates that the gage change point is in stand S2. Therefore, it initiates a stand speed change by moving the tap on potentiometer R2. This causes a tension change and stand S3 tension regulator TC3 operates on stand S3 to maintain set tension. When the transitional strip has passed through stand S2, the strip exiting the stand is at the correct gage and the stand drive is at the correct speed. The transition strip A H however, is now longer than it was at stand S1. This is a result of the reduction taken in stand S2 and is illustrated in FIG. 2. When the strip tracking system within the gage change sequencer 26 senses that the strip gage change point is at stand S3, it initiates astand S3 speed change and this is shown at point 1 in FIG. 2. Stand S4 tension controller TC4 now functions to maintain set tension between stands S3 and S4. At time t.,, the gage change point is at stand S4. The cylinder H5 of stand S5 now responds to maintain interstand tension between stands'S4 and S5 as previously described. However, and as explained above, an additional control signal may be involved on stand S5 speed. That is, the delivery thickness gage 42 operates into the stand S5 speed controller C5 and maintains set gage by varying the speed of stand S5. Therefore, at time t.,, the strip thickness reference to the gage control is changed to the revised value. This will, for the situation shown in FIG. 2, reduce the speed of stand S5, the effect being shown by the dotted line 40 in FIG. 2.

When the gage change point passes stand' S5 as shown at time in FIG. 2, the speed reference to stand S5 is changed. The strip thickness and speed will then be at the revised value for all five stands of the mill.- Table II above assumes a speed change for stand S5. In those applications where no gage control is used on stand S5 or where gage may be controlled by other means, stand S5 speed will not be changed until the gage change point passes stand S5 at time 13 in FIG. 2. In this case, the solid line for stand S5 speed applies as shown in FIG. 2.

The previous description in FIG. 2 applies to a situation where the delivered strip thickness changes to a thicker value. A similar description would apply to a situation where the delivered strip thickness changes to a thinner value except, of course, the gage is decreased in succession and the speed increased. It may be necessary'to revise the speed of all five stands in order to maintain the stand drafting constant. Small changes in schedule can be accommodated by revising only the speeds of stands S1 and S2 and allowing the interstand tension controllers to change the roll gaps of only stands S3, S4 and S5.

As was explained above, a situation may arise where several small coils of varying thicknesses are welded together and then rolled to a constant, delivered gage. The system of the invention can accept such a coil and roll it to the desired constant gage without interrupting the rolling process. The information locating the weld points must be provided via the gage sequencing circuit 26. These points determine the initiation of stand speed reference changes. The sequence of operation would then be the same as shown in FIG. 2.

Table III tabulates a case where input strip thickness changes from*4.0 MM to 4.4 MM, but the delivered thickness remains constant at 1 MM. The revised speeds for each stand are calculated based on maintaining the draft of each stand constant.

' TABLE 111 REVISED ROLLING SCHEDULE Multiply all drafts by 3.4/3.0 D, /D, Input gage changes from 4.0 MM and 4.4 MM and output gage remains at 1.0 MM

Stand D, H, S,

I 1.133 3.267 .306 2 1.133 2.134 .469 3 .68 1.454 .688 4 .34 .l .1 14 .90 5 +.l 14 1.0 1.00

initially changing the roll gap setting and speed of the first stand to change the gage of the strip material issuing from the first stand, and

in timed sequence changing the roll gap setting and speed of succeeding stands until all roll gap settings and speeds of the stands in the mill have been changed to accommodate a new gage, the roll gap setting and speed of each stand intermediate the first and last stands being changed following a change in the immediately preceding stand after a time interval substantially equal to .the time required for the strip to travel to each stand from its immediately preceding stand, and the speed of the last stand being changed when the speed of the next to the last stand is changed.

2. The method of claim 1 and including the step of measuring the gage at the output of said first stand, and varying the roll gap of said first stand as a function of variations in actual output gage at the first stand from desired output gage.

3. The method of claim 2 including the step of measuring actual output gage from the last stand of said 

1. In the method for changing the gage of strip material being rolled on a multi-stand tandem rolling mill while the strip material is moving through the mill, the steps of: initially changing the roll gap setting and speed of the first stand to change the gage of the strip material issuing from the first stand, and in timed sequence changing the roll gap setting and speed of succeeding stands until all roll gap settings and speeds of the stands in the mill have been changed to accommodate a new gage, the roll gap setting and speed of each stand intermediate the first and last stands being changed following a change in the immediately preceding stand after a time interval substantially equal to the time required for the strip to travel to each stand from its immediately preceding stand, and the speed of the last stand being changed when the speed of the next to the last stand is changed.
 2. The method of claim 1 and including the step of measuring the gage at the output of said first stand, and varying the roll gap of said first stand as a function of variations in actual output gage at the first stand from desired output gage.
 3. The method of claim 2 including the step of measuring actual output gage from the last stand of said rolling mill, and varying the speed of said last stand as a function of a deviation in actual output gage thus measured from desired output gage.
 4. The method of claim 3 wherein a gage change point on the strip material passes through successive stands of the mill as the roll gap setting and speed of successive stands are changed, and including the step of changing desired output gage as said gage change point passes through the next to the last stand. 